A LINC (Linear amplification with Nonlinear Components) method is known as a power amplification method used for amplifying, for example, a transmit signal in a communication device. In the LINC method, after an input signal having an envelope variation has been converted into two constant envelope signals having a phase difference corresponding to the amplitude of the input signal, each of the two constant envelope signals is amplified by using a nonlinear amplifier. Then, vector addition of the two amplified constant envelope signals is performed to obtain an amplified input signal. According to this method, because the nonlinear amplifier has only to amplify the constant envelope signals, a power-added efficiency may be improved (for example, refer to Patent Document 1).